What is the most important test before starting antibiotics for endocarditis?

• A. Blood cultures
• B. Echocardiogram
• C. CBC
• D. MRI brain

Answer: (D)

The most important test is blood cultures. Before starting antibiotics for suspected endocarditis, obtaining blood cultures from multiple sites helps identify the exact organism causing the infection and its antibiotic sensitivities. This information is essential to tailor therapy, choose the most effective and narrowest-spectrum antibiotics, and avoid unnecessary broad-spectrum use. Imaging like echocardiography is crucial for confirming endocarditis by showing vegetations and valve involvement, but it doesn’t tell you which microbe is causing the infection. A CBC can support the presence of infection but doesn’t identify the pathogen, and MRI of the brain is reserved for assessing neurological complications rather than guiding initial therapy.